Method and apparatus for minimizing the risk of air embolism when performing a procedure in a patient&#39;s thoracic cavity

ABSTRACT

An apparatus for minimizing the risk of air embolism includes an instrument delivery member  2  having a gas outlet  38  for delivering gas into a patient&#39;s thoracic cavity. The gas is directed across an opening  48  in the instrument delivery member  2  to help retain the gas in the patient&#39;s thoracic cavity. The gas is preferably carbon dioxide which is more soluble in blood than air which will thereby decrease the likelihood of the patient receiving an embolism due to trapped air in the patient&#39;s heart and great vessels after surgery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/209,558,filed Dec. 11, 1998 now U.S. Pat. No. 6,309,382, which is a divisionalof U.S. patent application Ser. No. 08/585,871, filed Jan. 16, 1996, nowissued as U.S. Pat. No. 5,849,005, which is a continuation-in-part ofU.S. patent application Ser. No. 08/485,600, filed Jun. 7, 1995 byinventors Garrison et al., now abandoned, and is related to U.S. patentapplication Ser. No. 08/415,366, filed Mar. 30, 1995 by inventorsStevens et al., now abandoned, the complete disclosures of which arehereby incorporated by reference for all purposes.

FIELD OF THE INVENTION

The present invention is directed to apparatus and methods forminimizing the risk of air embolism when performing a procedure in apatient's thoracic cavity. A specific application of the invention isdescribed in conjunction with devices and methods for repairing andreplacing a mitral valve in a patient's heart, however, the inventionmay be used in conjunction with any other procedure including repair orreplacement of mitral, aortic and other heart valves, repair of septaldefects, pulmonary thrombectomy, electrophysiological mapping andablation, coronary artery bypass grafting, angioplasty, atherectomy,treatment of aneurysms, myocardial drilling and revascularization, aswell as neurovascular and neurosurgical procedures.

BACKGROUND OF THE INVENTION

Various types of surgical procedures are currently performed toinvestigate, diagnose, and treat cardiovascular diseases. Using currenttechniques, many of these procedures require a gross thoracotomy,usually in the form of a median sternotomy, to gain access to thepatient's thoracic cavity. A saw is used to cut the sternumlongitudinally thereby allowing two opposing halves of the anterior orventral portion of the rib cage to be spread apart. A large opening inthe thoracic cavity is created through which the surgical team maydirectly visualize and operate upon the heart and other thoraciccontents.

Surgical intervention in the heart generally requires isolation of theheart and coronary blood vessels from the remainder of the arterialsystem and arrest of cardiac function. The heart is usually isolatedfrom the arterial system by introducing an external aortic cross-clampthrough a sternotomy and applying the clamp to the aorta between thebrachiocephalic artery and the coronary ostia. Cardioplegic fluid isthen injected into the coronary arteries, either directly into thecoronary ostia or through a puncture in the aortic root, to arrestcardiac function. In some cases, cardioplegic fluid is injected into thecoronary sinus for retrograde perfusion of the myocardium. The patientis then placed on cardiopulmonary bypass to maintain peripheralcirculation of oxygenated blood. Another method of arresting thepatient's heart is disclosed in U.S. Pat. No. 5,433,700, which isassigned to the assignee of the present application and is hereinincorporated by reference. U.S. Pat. No. 5,433,700 describes anendovascular catheter system for establishing arrest of cardiacfunction. The endovascular catheter system does not require a grossthoracotomy and facilitates less invasive methods of performingcardiopulmonary procedures.

Once the patient is placed on cardiopulmonary bypass, various surgicaltechniques may be used to repair a diseased or damaged valve, includingannuloplasty (contracting the valve annulus), quadrangular resection(narrowing the valve leaflets), commissurotomy (cutting the valvecommissures to separate the valve leaflets), shortening mitral ortricuspid valve chordae tendonae, reattachment of severed mitral ortricuspid valve chordae tendonae or papillary muscle tissue, anddecalcification of valve and annulus tissue. Alternatively, the valvemay be replaced, by excising the valve leaflets of the natural valve andsecuring a replacement valve in the valve position usually by suturingthe replacement valve to the natural valve annulus. Various types ofreplacement valves are in current use, including mechanical andbiological prostheses, homografts, and allografts, as described inBodnar and Frater, Replacement Cardiac Valves 1-357 (1991), which isincorporated herein by reference. A comprehensive discussion of heartvalve diseases and the surgical treatment thereof is found in Kirklinand Barratt-Boyes, Cardiac Surgery, pp. 323-459 (1986), the completedisclosure of which is incorporated herein by reference.

The mitral valve, located between the left atrium and left ventricle ofthe heart, is most easily reached through the wall of the left atrium,which normally resides on the posterior side of the heart, opposite theside of the heart that is exposed by a median sternotomy. Therefore, inorder to access the mitral valve via a sternotomy, the heart is rotatedto bring the left atrium into an anterior position accessible throughthe sternotomy. An opening, or atriotomy, is then made in the right sideof the left atrium, anterior to the right pulmonary veins. The atriotomyis retracted by means of sutures or a retraction device, exposing themitral valve directly posterior to the atriotomy. One of theaforementioned techniques may then be used to repair or replace thevalve.

An alternative technique for mitral valve access may be used when amedian sternotomy and/or rotational manipulation of the heart areundesirable. In this technique, a large incision is made in the rightlateral side of the chest, usually in the region of the fifthintercostal space. One or more ribs may be removed from the patient, andother ribs near the incision are retracted outward to create a largeopening into the thoracic cavity. The left atrium is then exposed on theposterior side of the heart, and an atriotomy is formed in the wall ofthe left atrium, through which the mitral valve may be accessed forrepair or replacement.

Using such open-chest techniques, the large opening provided by a mediansternotomy or right thoracotomy enables the surgeon to see the mitralvalve directly through the left atriotomy, and to position his or herhands within the thoracic cavity in close proximity to the exterior ofthe heart for manipulation of surgical instruments, removal of excisedtissue, and/or-introduction of a replacement valve through the atriotomyfor attachment within the heart. However, these invasive, open-chestprocedures produce a high degree of trauma, a significant risk ofcomplications, an extended hospital stay, and a painful recovery periodfor the patient. Moreover, while heart valve surgery produces beneficialresults for many patients, numerous others who might benefit from suchsurgery are unable or unwilling to undergo the trauma and risks ofcurrent techniques.

A problem which occurs in conventional open-heart procedures is that airenters the heart during the procedure and must be removed from the heartafter completing the procedure. Air which remains in the circulatorysystem after the heart is closed may produce air emboli which couldtravel to the brain and cause a stroke or death. Conventional de-airingtechniques include mechanical manipulations and venting of the heart toremove air trapped in the heart. U.S. Pat. No. 5,370,631, for example,discloses an apparatus for de-airing the heart which includes aslotted-needle and a resilient bulb.

Carbon dioxide has been used to displace air in the patient's thoraciccavity to help prevent air emboli. In animal studies, carbon dioxide hasbeen shown to be as much as twelve times more soluble in blood than air.Thus, displacing air with carbon dioxide may be beneficial in reducingthe harmful effects of gas emboli.

In open-heart procedures, carbon dioxide has been introduced into thethoracic cavity through the median sternotomy. Since the patient's chestis open, the carbon dioxide in the chest cavity readily disperses out ofthe chest and, therefore, carbon dioxide must be continuously orperiodically replaced, Ng and Rosen, “Carbon Dioxide in the preventionof air embolism during open-heart surgery”, Thorax 23:194-196 (1968).

Thus, a problem with previous use of carbon dioxide in open heartprocedures is that air is free to enter the open chest cavity and highcarbon dioxide concentrations cannot be maintained in the chest cavityfor extended periods of time without requiring continuous or periodicinjection of carbon dioxide.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, methods andapparatus for reducing the risk of air embolism when performing aprocedure in a patient's thoracic cavity are provided. In an aspect ofthe present invention an instrument delivery member is inserted into apatient's thoracic cavity between adjacent ribs thereby forming apercutaneous intercostal penetration. The instrument delivery member hasa gas outlet for injecting a gas, preferably carbon dioxide, into thepatient's thoracic cavity. The gas displaces air from the patient'sthoracic cavity thereby reducing the risk of air emboli. The instrumentdelivery member also has a throughhole sized to permit an instrument topass therethrough.

The present invention is particularly useful when performing the mitralvalve replacement and repair procedures described in U.S. patentapplication Ser. No. 08/485,600 and U.S. patent application Ser. No.08/163,241 both of which are assigned to the assignee of the presentapplication and which are incorporated herein by reference. The methodsfacilitate surgical intervention within the heart or great vesselswithout the need for a gross thoracotomy. The procedure is carried outthrough small incisions within intercostal spaces of the rib cagewithout cutting, removing, or significantly deflecting the patient'sribs or sternum thereby reducing the trauma, risks, recovery time andpain that accompany conventional techniques. The devices and methodspermit removal of tissue from the thoracic cavity and introduction ofsurgical instruments, replacement valves and the like into the thoraciccavity, to facilitate heart valve repair and replacement. The devicesand methods facilitate replacement of a heart valve with various typesof prostheses, including mechanical and biological prostheses,homografts, and allografts.

In a preferred embodiment of the present invention, the instrumentdelivery member includes a plurality of gas outlets which are angledtoward the distal end to help retain gas in the patient's thoraciccavity. In an alternative embodiment, the gas outlets are angledsubstantially perpendicular to the longitudinal axis of the instrumentdelivery member with the gas passing adjacent the distal end. A vacuumpump may also be provided for withdrawing air from the patient'sthoracic cavity or for capturing gas escaping from the patient'sthoracic cavity.

The concentration of gas in the patient's thoracic cavity is preferablymonitored so that a threshold gas concentration is maintained. Whenusing carbon dioxide, the gas concentration is preferably at least 70%and more preferably at least 90% by volume. Alternatively, the airconcentration may be maintained at no more than 50% and more preferablyno more than 5% by volume. The humidity and temperature in the patient'sthoracic cavity are also preferably monitored to maintain a desirablehumidity and temperature. The relative humidity in the patient'sthoracic cavity is preferably at least 10% and more preferably at least50%. The temperature of the gas is also preferably maintained at atemperature below body temperature and preferably below 20 (degrees) C.

The pressure of the gas in the patient's thoracic cavity is alsopreferably monitored and regulated. The gas pressure is preferablymaintained at a pressure higher than the pressure outside the thoraciccavity to prevent air does from entering the thoracic cavity. Whenperforming the procedure described in U.S. patent application Ser. No.08/485,600, which is incorporated herein by reference, a number ofinstrument delivery members, such as cannulas or trocars, are insertedinto the patient to perform a mitral valve procedure. The presentinvention provides seals at the instrument delivery members to preventthe escape of gas so that the pressure can be maintained in the thoraciccavity. Such seals are commonly used in laparoscopic procedures. Unlikelaparoscopic surgery, however, the pressure in the thoracic cavity isnot used to retract the thoracic cavity and, as such, the pressure inthe thoracic cavity is kept between 1 and 14 mm Hg and more preferablybetween 1 and 10 mm Hg and most preferably between 1 and 8 mm Hg all ofwhich are below the pressures used in laparoscopic procedures which aretypically between 15 and 20 mm Hg.

In another aspect of the present invention, the instrument deliverymember includes a gas inlet and a gas outlet positioned to receive gasissuing from the gas inlet. The gas passing from the gas inlet to thegas outlet preferably passes across the throughhole, and preferablytransects the throughhole, to act as a gas shield which minimizes gaslosses through the instrument delivery member. The gas shieldadvantageously permits the introduction of instruments through theinstrument delivery member without significantly hindering use ofinstruments. The gas which is used for the gas shield may be any gassuch as carbon dioxide or air. A blower, fan or compressor is coupled tothe gas inlet and may also be coupled to the gas outlet for closedcircuit circulation.

In yet another aspect of the invention, a vent is provided for ventinggas from the left ventricle when performing a procedure on the patient'sheart such as a mitral valve repair or replacement. The vent includesfirst and second lumens and first and second outlets fluidly coupled tothe first and second lumens, respectively. The first lumen and firstoutlet are used for injecting gas into the patient's heart and forevacuating gas from the heart when the heart is being closed after themitral valve replacement or repair procedure. The second lumen andsecond outlet are used for sampling gas in the patient's thoraciccavity.

In a specific application of the vent, the vent is positioned in theleft ventricle and a gas, such as carbon dioxide, is injected into thepatient through the first lumen. The gas displaces air in the leftventricle so that when the heart is closed the presence of air isminimized to minimize the risk of air emboli. The gas is preferablyinjected into the heart using the temperature, pressure, humidity andgas concentration monitoring and control system described above. Whenthe heart is closed, the first lumen and first outlet are used toevacuate gasses from the heart. The second outlet and second lumen areused to collect gasses in the thoracic cavity for measuring pressure,temperature, humidity, and/or gas concentrations. The second outlet isspaced apart from the distal end so that the measurements are not overlyinfluenced by the gas being injected into the left ventricle through thefirst lumen and first outlet.

In yet another aspect of the invention, an enclosure is provided aroundthe patient for providing a sealed operating space. A gas, such ascarbon dioxide, is maintained in the sealed operating space so that airdoes not enter the patient's cardiopulmonary system during a medicalprocedure. The enclosure includes a seal, such as a drape, which engagesthe patient and provides a substantially air tight seal. The enclosureincludes arm pass-throughs which are used by the surgeon to perform themedical procedure in the enclosure. An advantage of the enclosure isthat it may also be used in conventional open heart procedures since agas environment is created around the patient.

The terms “percutaneous intercostal penetration” and “intercostalpenetration” as used herein refer to a penetration, in the form of asmall cut, incision, hole, or the like through the chest wall betweentwo adjacent ribs, wherein the patient's rib cage and sternum remainsubstantially intact, without cutting, removing, or significantlydisplacing the ribs or sternum. These terms are intended to distinguisha gross thoracotomy such as a median sternotomy, wherein the sternumand/or one or more ribs are cut or removed from the rib cage, or one ormore ribs are retracted significantly, to create a large opening intothe thoracic cavity. It is understood that one or more ribs may beretracted or deflected a small amount and/or a small amount ofintercostal cartilage may be removed without departing from the scope ofthe invention.

These and other advantages of the invention will become apparent fromthe following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. shows a patient prepared for a mitral valve replacement with anumber of instrument delivery members extending into the patient'sthoracic cavity and a gas delivery system coupled to one of theinstrument delivery members;

FIG. 2 shows a cross-sectional view of the patient of FIG. 1 with a gasoutlet coupled to one of the instrument delivery members for injecting agas into the patient's thoracic cavity;

FIG. 3 is an isometric view of the instrument delivery member having agas delivery assembly;

FIG. 4. is an isometric view of the gas delivery assembly of FIG. 3;

FIG. 5 is a cross-sectional view of a second preferred embodiment of theinstrument delivery member;

FIG. 6 is an end view of the instrument delivery member of FIG. 5:

FIG. 7 is a cross-sectional view of a gas path showing the orientationof a gas outlet of the instrument delivery member of FIG. 5;

FIG. 8 is a cross-sectional view of a patient with a vent extendingthrough the instrument delivery member and into the patient's leftventricle;

FIG. 9 is a plan view of the vent of FIG. 8;

FIG. 9A is a side view of an alternate embodiment of the left ventriclevent of FIG. 9;

FIG. 10 is a side view of the vent of FIG. 8;

FIG. 11 is a cross-sectional view of the vent of FIG. 8 showing firstand second lumens;

FIG. 12 is a view looking through the instrument delivery member with amitral valve being attached to the patient's valve annulus;

FIG. 13 shows vent catheters extending through a lumen of an endoaorticpartitioning catheter;

FIG. 14 is an isometric view of another preferred instrument deliverymember having a gas inlet and a gas outlet positioned to receive gasissuing from the gas inlet;

FIG. 15 is a top view of the instrument delivery member of FIG. 14;

FIG. 16 is a schematic of the gas delivery system, monitoring system andcontrol system;

FIG. 17 is a view looking through the instrument delivery member with anatriotomy being closed and a vent extending through the atriotomy; and

FIG. 18 is an isometric view of an enclosure extending around a patient.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring to FIG. 1, a system for minimizing the risk of air emboli whenperforming a procedure in a patient's thoracic cavity is shown. Aspecific application of the invention is developed herein with respectto a minimally invasive mitral valve replacement procedure, however, theapparatus and methods of the present invention may be used inconjunction with any other procedure including repair or replacement ofaortic and other heart valves, repair of septal defects, pulmonarythrombectomy, electrophysiological mapping and ablation, coronary arterybypass grafting, angioplasty, atherectomy, treatment of aneurysms,myocardial drilling and revascularization, as well as neurovascular andneurosurgical procedures. The procedure for performing the minimallyinvasive mitral valve repair and replacement will be discussed to theextent necessary to adequately describe the present invention and acomplete discussion is provided in U.S. patent application Ser. No.08/485,600, filed Jun. 7, 1995, which is incorporated herein byreference.

Referring still to FIG. 1, an instrument delivery member 2 includes athroughhole 4 for introduction of surgical instruments into a patient'sthoracic cavity. The instrument delivery member 2 is preferably a hollowtube, such as a cannula, trocar sleeve, a 3-sided channel-shaped member,a ring retractor, a wound retractor having a pair of adjustable parallelblades, or any other device which facilitates introduction of a medicalinstrument into a patient between adjacent ribs. The instrument deliverymember 2 is positioned between adjacent ribs in the patient and a numberof other instrument delivery members 6-10 are positioned at variousother positions thereby forming a number of percutaneous intercostalpenetrations.

A retractor 12 passes through instrument delivery member 9 and varioussensors 13, which are described in greater detail below, pass throughinstrument delivery member 6. A thoracoscope 14 passes throughinstrument delivery member 8 and is coupled to a monitor 16 for viewingthe patient's thoracic cavity. Any other viewing device may be used inconjunction with, or as a substitute for, the thoracoscope 14. A firstremovable plug 18 is positioned in the delivery member 7 with the firstplug 18 separated from the instrument delivery member 7 for clarity. Areplacement valve 20 is mounted to a holder 22, however, a repairdevice, such as a ring for annuloplasty, may, of course, be used whenrepairing rather than replacing the mitral valve.

A gas delivery system 24 is coupled to the instrument delivery member 2for delivering a gas into the patient's thoracic cavity. The gasdelivery system 24 supplies gas, such as carbon dioxide, forintroduction into the patient's thoracic cavity to minimize the risk ofan air embolism when performing a procedure in the patient's thoraciccavity. A monitoring system 26 is coupled to the sensors 13 formonitoring the various conditions sensed by the sensors 13. A controlsystem 28 receives the information from the sensors 13 via themonitoring system 26 and sends control information to the gas deliverysystem 24 based upon the sensor data. The gas delivery system 24,control system 28 and monitoring system 26 are described in greaterdetail below in connection with FIG. 16.

A vacuum pump 30 is coupled to the instrument delivery member 9 havingthe retractor 12 for withdrawing air from the thoracic cavity when thegas is injected into the thoracic cavity. The vacuum pump 30 is alsocoupled to a line 32 which is positioned adjacent to the instrumentdelivery member 2 for withdrawing gas which escapes through theinstrument delivery member. A vent needle 34 extends through theinstrument delivery member 10 and into the patient used for ventinggasses from the thoracic cavity as described in further detail below.

Referring to FIG. 2, a cross-sectional view of the patient is shown. Thevent needle 34 is preferably perforated along the longitudinal axis (notshown) of the needle for venting gasses from the left ventricle. Use ofthe vent needle 34 is described in greater detail below in connectionwith preferred methods of operation. The retractor 12 engages anatriotomy AI formed in the patient's heart for retracting the atriotomyopen. A number of sutures 36 extend through the instrument deliverymember 2 and are used for attaching the repair valve in the mannerdescribed in U.S. patent application Ser. No. 08/485,600.

The instrument delivery member 2 includes a gas outlet 38, preferably anumber of gas outlets, and a gas inlet 40 coupled to the gas deliverysystem 24 for delivering the gas into the thoracic cavity. A gas, suchas carbon dioxide, is introduced into the patient's thoracic cavitythrough the gas outlet 38. Referring to FIGS. 3 and 4, the instrumentdelivery member 2 and a gas delivery assembly 42 are shown. Theinstrument delivery member 2 preferably includes a sidewall 44 and thethroughhole 4 defines a longitudinal axis 46. The throughhole 4 extendsfrom a proximal end and terminates at an opening 48 at a distal end 50.Although the instrument delivery member 2 preferably has an ovalthroughhole, any other cross-section may be used such as a race-track,rectangular, trapezoidal, elliptical or circular cross-sectional shape.

The throughhole 4 is preferably sized to allow an annuloplasty ring orreplacement valve mounted on a holder to pass therethrough. Thethroughhole 4 preferably has a cross-sectional shape having a width ofpreferably about 10-30 mm, and more preferably 15-25 mm, and a height ofpreferably about 25-75 mm, more preferably 30-50 mm. Furthermore, thewidth or height of the throughhole is preferably at least 2 cm, morepreferably at least 2.5 cm and most preferably at least 3 cm. Typicallaparoscopic trocars have much smaller openings since gas losses must beminimized when operating at the higher pressures used in laparoscopicprocedures. The exact width and height will often be determined by thewidth (or diameter) and height of the annuloplasty ring or replacementvalve and holder being used in the procedure. It is sometimes desirableto begin the procedure with a instrument delivery member 2 of theminimum size necessary to assess the condition of the native valve. Forexample, an instrument delivery member 2 having a width of about 15-20mm may be used initially. When the size of the annuloplasty ring orprosthetic valve has been selected, the smaller instrument deliverymember may be replaced, if necessary, with a larger instrument deliverymember to accommodate the prosthesis.

The instrument delivery member 2 is configured for placement in anintercostal space preferably without retraction of ribs, or at leastminimal retraction of ribs, and preferably has an external width of lessthan about 30 mm, and preferably less than about 25 mm. Although it ispreferred to provide a sidewall 44 which has an elongate tubularstructure with a length sufficient to extend into the thoracic cavity,the sidewall may simply be the elements of a ring retractor or any ofthe other instrument delivery members described above so long as theinstrument delivery member provides access to the patient's thoraciccavity for surgical instruments. The instrument delivery member has aflange 52 at its proximal end which engages the outside of the patient'schest. The instrument delivery member 2 has a length sufficient toextend from outside of the chest, through the intercostal space, andinto the chest cavity just beyond the interior of the chest wall. Theinstrument delivery member 2 preferably has a length of about 20-70 mmand more preferably about 30-50 mm from the flange 52 to the distal end.

The instrument delivery member 2 includes a suture organizing ring 54attached to the flange 52. Organizing ring 54 has a plurality ofcircumferentially-spaced radial slots 56 or suture holders in which asuture thread may be received and retained. Slots 56 have tapered upperends 58 for guiding a suture thread to the slot. Suture organizing ring54 allows sutures placed in the heart for attachment of a prosthesis tobe drawn through the throughhole and temporarily placed in slots 56 tokeep the sutures individually separated and untangled. In order tofacilitate introducing instrument delivery member 2 through a punctureor small incision between the ribs, an obturator (not shown) may beinserted into the throughhole 4. The instrument delivery member 2 mayalso be made of a flexible or deformable material to allow it to beshaped by the user or to conform to the shape of the intercostal space.

Still referring to FIGS. 3 and 4, the gas delivery assembly includes asleeve 60 which clips onto the sidewall 44. The sidewall 44 may includeribs (not shown) for enhanced engagement with the gas delivery assembly42. The gas outlet 38, and preferably a plurality of gas outlets, areprovided on a horseshoe-shaped ring 61. The gas delivery assembly 42 ismounted to the sidewall 44 so that a plurality of gas outlets 38 aredirected across the opening 48. In the preferred embodiment, the opening48 lies in a plane perpendicular to the longitudinal axis 46 so that thegas outlets 38 are also directed substantially perpendicular to thelongitudinal axis. The opening 48 may also be skewed with respect to thelongitudinal axis with the gas outlets 38 also being skewed so that thegas outlets 38 are configured to issue gas directly across the opening48. By orienting the gas outlets 38 in this manner, the gas injectedinto the patient helps retain the gas in the thoracic cavity by creatinga gas curtain at the opening 48 of the instrument delivery member.Although it is preferred to provide one gas delivery assembly, two ormore gas delivery assemblies may be provided. Furthermore, although itis preferred to direct the gas in a direction perpendicular to thelongitudinal axis 46, the gas outlets 38 may also be angled toward thedistal end or, alternatively, angled toward the proximal end with abaffle to redirect the gas so that the gas does not simply exit throughthe proximal opening in the instrument delivery member 2. Finally, thegas outlets 38 are preferably positioned so that they direct gas acrosssubstantially the entire width or height of the throughhole 4 so thatgas losses through the throughhole are minimized.

A plug 62 is removably mounted to the instrument delivery member 2 toclose, or at least partially close, the throughhole 4 thereby minimizinggas losses through the throughhole 4. The second plug 62 preferablyincludes a resilient surface 63, preferably an elastic band, whichengages the instrument delivery member 2 to provide a snug fit whensutures are positioned through the throughhole 4. The second plug 62 hasan opening 64 so that instruments may still be passed through thethroughhole while reducing losses through the throughhole. A third plug66 closes the opening 64 so that substantially all gas losses throughthe throughhole 4 are eliminated. Alternatively, a number of differentplugs having different sized openings, or no openings at all like secondplug 62A, may be provided. Furthermore, the opening 64 may be any othershape such as H-shaped, an oval ring, Z-shaped or a FIG. “8.”

Referring to FIGS. 5-7, another instrument delivery member 2A is shownwhich includes integrally formed gas outlets 38A wherein similarreference numbers are used to represent similar features described inthe embodiment of FIGS. 3-4. The discussion above concerning instrumentdelivery member 2 is equally applicable here and the preferred featuresfor the instrument delivery member 2 are also preferred with theinstrument delivery member 2A.

The instrument delivery member 2A includes a gas inlet 66 configured tobe coupled to a gas line 68 which, in turn, is coupled to the gasdelivery system 24. The instrument delivery member 2A includesintegrally formed gas outlets 38A whereas the instrument delivery member2 includes the removable gas delivery assembly 42. The gas inlet 66 iscoupled to a chamber 70 which extends circumferentially around theinstrument delivery member 2A between an inner wall 72 and an outer wall74. A plurality of gas channels 74 extend from the common chamber 70 and76 terminate at the gas outlets 38A which direct the gas in thedirection of arrows 78. The gas outlets 38A are preferably directedtoward the distal end and, further, are directed toward the middle ofthe instrument delivery member 2A. The gas outlets 2A cooperate with oneanother to hinder escape of gasses through the instrument deliverymember 2A.

The gas outlets 38A are particularly useful for providing a pressure inthe thoracic cavity above the pressure outside the thoracic cavity tohelp keep air out of the thoracic cavity. Although it is preferred toangle the gas outlet 38A toward the distal end, the gas outlet 38A maybe oriented in any other manner so long as the gas outlet 38A tends toprevent gas from escaping through the open proximal end of theinstrument delivery member 2A. Furthermore, although it is preferred toprovide a number of gas outlets 38A around the entire periphery of theinstrument delivery member 2A, the gas outlets 38A may also be providedonly along a section of the instrument delivery member 2A.

Referring to FIG. 8, a cross-sectional view of the patient is shown witha vent 78 extending into the left ventricle LV. The vent 78 preferablyhas a distal end 80 which extends to the apex of the left ventricle LVfor venting the left ventricle LV. The distal end 80 preferably includesa soft tip for preventing trauma to the left ventricle. The first outlet86 is preferably used for injecting gas into the left ventricle and forventing gas from the left ventricle. The second outlet is preferablycoupled to a monitoring system 26 for monitoring the conditions in thepatient's thoracic cavity such as the gas concentration, humidity,temperature and pressure. Use of the vent 78 is described below inconnection with discussion of preferred methods of present invention.

Referring to FIGS. 9-11, a distal portion 81 of the vent 78 is shown ina natural, unbiased shape. The distal portion 81 of the vent 78 isconfigured to position the distal end 80 at the apex of the leftventricle LV when the proximal portion extends through the valveannulus. The approximate position of the valve annulus is shown atbroken line 79 which also indicates the beginning of the distal portion81. The vent 78 preferably includes a first lumen 82, a second lumen 84and first and second outlets 86, 88 fluidly coupled to the first andsecond lumens 26, respectively. The first and second outlets 86, 88 arepreferably spaced apart between 0.5 and 8 cm, and more preferablybetween 2 and 4 cm, so that gas samples taken through the first outletare not overly influenced by gas injected into the left ventriclethrough the first outlet 88. The first outlet 86 is preferablypositioned near the distal end 80 and the second outlet 88 is preferablybetween at least 0.5, more preferably at least 5 cm and most preferablyat least 8 cm from the distal end. The distal portion 81 preferablyextends between 1 and 10 cm, and more preferably between 1 and 5 cm inthe axial direction A, and extends in the radial direction B between 0and 15 cm and more preferably 2 and 8 cm, and extends between 0 and 5 cmand more preferably between 0.5 and 3 cm in the other radial directionC. The proximal end of the vent 78 is flexible so that the user mayposition the vent 78 where it will not interfere with the medicalprocedure. Referring to FIG. 9A, the distal end of another leftventricle vent 78A is shown. The left ventricle vent 78A has the samepreferred dimensions as the left ventricle vent 78, however, the firstand second outlets 86A, 88A are both positioned near the proximal endwith an angle D therebetween. The angle D is preferably at least 90degrees and preferably greater than 90 degrees so that gas issuing fromthe first outlet 86A does not overly influence gas samples taken atsecond outlet 88A.

Referring to FIGS. 12, a view through the throughhole 4 of theinstrument delivery member 2 is shown. A spacer 98 prevents contactbetween the valve 20, which in this case is a mechanical valve, and thevent 78. The spacer 98 preferably includes a pair of holes 100 forremoving the spacer 98 before closing the heart. Alternatively, thespacer 98 may be dispensed with and the vent 78 may be coated with alubricious coating of silicone, teflon or polyurethane to prevent damageto the valve 20 when the vent 78 is withdrawn. The instrument deliverymember 2 includes a clip 102 for holding the vent 78 after the vent 78is positioned in the left ventricle LV. The clip 102 prevents movementof the vent 78 and also positions the vent 78 away from the center ofthe throughhole 4 so that other instruments may be used through theinstrument delivery member 2.

Referring to FIG. 13, a left ventricle vent 104 and an aortic vent 106are shown extending through an endoaortic partitioning catheter 108which is described in U.S. patent application Ser. No. 08/415,366 toStevens et al. which is assigned to the assignee of the presentinvention and which is incorporated herein by reference. The endoaorticpartitioning catheter 108 has an occluding member 110 which occludes theascending aorta. Cardioplegic fluid is introduced to the coronaryarteries through the endoaortic partitioning catheter 110 for arrestingcardiac function. The endoaortic partitioning catheter 110 provides aworking lumen (not shown) through which instruments, such as the leftventricle vent 104 and aortic vent 106, may pass.

The aortic vent 106 has a curved distal end 112 which generally conformsto the shape of the occluding member 110 for venting gasses around theoccluding member 110. The aortic vent 106 has an opening 114 at thedistal end 112 for venting gasses from the ascending aorta AO. Theproximal end of the aortic vent 106 is relatively stiff so that theaortic vent 106 may be rotated from the proximal end. Rotation of theaortic vent causes the distal end 112 to circumscribe the outer surfaceof the occluding member 110 for venting gasses around the occludingmember 110. When using the aortic vent 106, the patient is preferablytilted feet downward so that gasses in the ascending aorta rise towardthe occluding member 10 for venting.

The left ventricle vent 104 has an opening 116 near a curved, distal end118 for venting the left ventricle. The curved end 118 prevents damageto the aortic valve and the left ventricle when the left ventricle vent104 passes through the aortic valve and the left ventricle. The curveddistal end 118 is preferably curved in an arc greater than 180° so thatthe curved portion also contacts the aortic valve when the catheter iswithdrawn. Use of the aortic vent 106 and left ventricle vent 104 isdescribed below in connection with preferred methods of the presentinvention. Both the aortic vent 106 are and the left ventricle vent 104are preferably coupled to the vacuum pump 30 for withdrawing gasses fromthe patient's heart.

Referring to FIGS. 14 and 15, another instrument delivery member 2B isshown which includes both a gas inlet 120 and a gas outlet 122. Theinstrument delivery member 2B is substantially the same as theinstrument delivery members 2 and 2A described above and discussion ofthe features of the instrument delivery members 2 and 2A are equallyapplicable here. The gas outlet 122 is positioned to receive gas issuingfrom the gas inlet 120 so that a gas shield is formed which minimizesescape of gasses from the thoracic cavity. The gas inlet and outletpreferably extend across substantially the entire width and/or length ofthe throughhole 4 and include tapered entrances 124, 126 so that alaminar flow of gas is achieved. The bottom surfaces of the gas inletand outlet 120, 122 are preferably flush with the flange 52 so that theflange 52 helps provide the gas shield across the throughhole 4. The gasinlet 120 preferably has a relatively small internal height of between0.25 and 5 mm and more preferably between 0.5 and 3 mm. The gas outlet122 may have a somewhat larger internal height of preferably between 1and 10 mm and more preferably between 2 and 5 mm. The gas outlet 122 ispreferably positioned and sized to withdraw substantially all of the gasissuing from the gas inlet 122 so that a gas shield is maintained acrossthe throughhole 4.

The gas inlet and outlet 120, 122 are coupled to a fan, blower orcompressor (not shown) for delivering the gas and forming the gas shieldwith a closed system. A filter (not shown), preferably a hydrophobicfilter, filters the gas in the closed system. The gas used for the gasshield may be any gas, such as carbon dioxide or even air, since the gasshield primarily functions to reduce gas losses through the instrumentdelivery member 2B. The gas shield may be formed with carbon dioxidewith the outlet 122 delivering the carbon dioxide into the patient. Forexample, the instrument delivery member 2B may include the gas deliveryassembly 42 with the gas delivery assembly 42 being coupled to theoutlet 122. Thus, although the instrument delivery member 2B is anindependent device for minimizing gas losses from the patient's thoraciccavity, the gas inlet and gas outlet 120, 122 may also be used inconnection with the embodiment of FIGS. 3-4 and 5-7 so that gas isinjected into the patient with the same member that is used for formingthe gas shield. Although it is preferred to provide the gas inlet 120 ata geometrically opposite side of the instrument delivery member 2B fromthe gas outlet 122, the instrument delivery member 2B may includebaffles and the like so that the gas outlet 122 is not positionedgeometrically opposite the gas inlet 120 but, nonetheless, receives thegas issuing from the gas inlet 120. Furthermore, although it ispreferred to provide the gas inlet and outlet 120, 122 near the proximalend, the gas inlet and outlet may also be positioned near the distal endof the instrument delivery member 2B similar to orientation of the gasdelivery assembly 42.

Referring to FIG. 16, the gas delivery system 24, monitoring system 26and control system 28 are shown. The monitoring system 26 preferablyincludes a temperature sensor 128, a humidity sensor 130, a pressuresensor 132 and a gas sensor 134 such as a carbon dioxide or oxygensensor. Referring to FIG. 1, the sensors 128, 130, 132, 134 extendthrough the instrument delivery member 6, however, more than one of theinstrument delivery member may be used for the sensors 13 if necessary.Alternatively, a sampling tube, such as any of the vents describedherein, may be periodically or continuously positioned within thepatient for sampling gas which is then delivered to the various sensorsoutside of the patient. The temperature and humidity sensors 128 arealso coupled to the gas delivery line for measuring the temperature andhumidity of the gas before injection into the patient's thoracic cavity.

The gas delivery system 24 includes a source of gas 136, such as carbondioxide, a heater and/or cooler 138, a humidifier 140 and a source oftherapeutics 142. Although it is preferred to use carbon dioxide anyother suitable gas may be used which is absorbed by the body morereadily than air so that the risk of harm due to gas emboli is reduced.A discharge valve or regulator 144, which is controlled by the controlsystem 28, controls the flow of gas. The heater/cooler 138 is coupled tothe discharge line for heating and/or cooling the gas. A valve 146regulates the amount of heated or cooled gas added to the gas line fromthe source of gas 136. It is preferred to cool the gas since lowertemperatures are advantageous when performing procedures on the heartand because cooling the gas increases the gas density which may furtherreduce gas losses from the thoracic cavity. Although it is preferred toprovide a separate heating and cooling branch, the entire flow of gasfrom the source of gas 136 may be passed through the heater/cooler 138rather than only a portion of the gas stream. Valves 144, 146 and 147for regulating the gas stream are controlled by the control system 28.The monitoring system 26 may also include a flow rate indicator (notshown) for measuring the flow rate downstream from the valve 147.

The humidifier 140 prevents excessive drying of the patient's tissueduring the medical procedure. In a preferred method described below, thethoracic cavity is flooded with gas throughout the procedure which mightexcessively dry the patient's tissue. In order to prevent excess drying,the humidifier 140 adds water vapor to the gas stream. The humidifier140 may be any conventional humidifier such as a misting nozzle, amixing chamber, or an atomizer. The humidifier 140 preferably drawsliquid from a source of sterilized saline or water (not shown). A valve148, which is controlled by the control system 28, regulates theaddition of humidified gas to the gas stream in response to the humiditymeasurements by the humidity sensor 130.

The source of therapeutics adds therapeutic agents, such asanti-inflammatories, to the gas stream for, for example, reducing postoperative adhesions. A surfactant may also be introduced into thepatient's thoracic cavity before filling the heart with blood to reducethe surface tension of bubbles in the heart. A preferred surfactantwould be the phospholipid pulmonary surfactant found in the lungs.Reduction of the surface tension facilitates removal of gasses since gasbubbles are less likely to adhere to the heart and other vessels andwill pool at locations where the various vents may be used. Othertherapeutics which might be delivered include topical anesthetics. Theintroduction of therapeutics is regulated by a valve 150 which iscontrolled by the control system 28.

The monitoring system 26 includes the temperature, humidity, pressureand gas concentration sensors 128, 130, 132, 134. Referring to FIG. 1,the sensors 13 have lines which lead to the thoracic cavity which may beelectrical wires, when using a pressure transducer for example, or maybe sample lines which withdraw gas from the thoracic cavity and aresampled outside the body. A single sample line may branch off to thevarious sensors or, alternatively, the sensors may be connected togetherin series. As mentioned above, the left ventricle vent 104 may becoupled to any of the sensors for measuring various parameters in thethoracic cavity. Referring again to FIG. 16, the gas sensor detects theconcentration of the gas injected into the thoracic cavity or,alternatively, detects the concentration of air remaining in thethoracic cavity. When using carbon dioxide, the gas concentration sensor134 is preferably a sensor with the ability to measure 0-100% carbondioxide concentration in a gas sample at 1-2 atm pressure, 0-37(degrees) C. and up to 90% relative humidity with a response time ofless than about 60 seconds. If necessary for accuracy, the sensor mayrequire that the sample is dried with a dehumidifier (not shown). Anumber of conventional carbon dioxide sensors may be used which useinfra-red sensors, mass spectroscopy, thermal conductivity andelectrochemical cell sensors, laser absorption and emissiontechnologies.

The control system 28 receives data from the sensors 13 and is coupledto the various parts of the gas delivery system 24 for controlling thedelivery of gas. The control system 28 preferably includes a display 152for visual indication of the various sensor data such as pressure,temperature, humidity, and gas concentration in the patient's thoraciccavity as well as the gas flow rate into the patient. The control system28 also preferably includes one or more alarms 154 which indicate whenthe temperature, humidity, pressure, gas concentration and/or gas flowrate is at an unacceptable level. The alarm 154 may be any conventionalalarm such as a visual and/or audible alarm. The control system 28 ispreferably adapted to maintain the temperature, humidity, pressureand/or gas concentration at predetermined values. Although it ispreferred to provide the entire monitoring system 26, individual piecesof the gas delivery system 24 and monitoring system 26 may be usedwithout departing from the scope of the present invention. Furthermore,although it is preferred to provide a combined system, the variouscomponents may, of course, also be provided separately.

Preferred methods of the present invention will now be described inconnection with the preferred embodiments. It is understood that thepreferred embodiments provide preferred apparatus for performing themethods of the present invention, however, other apparatus may be usedwithout departing from the scope of the invention as defined by theclaims. The following preferred methods are described in connection witha mitral valve replacement or repair, however, any of the otherprocedures mentioned above may also be performed without departing fromthe scope of the invention. A complete discussion of a preferred methodof mitral valve replacement is described in U.S. patent application Ser.No. 08/485,600, filed Jun. 7, 1995.

The patient is prepared for surgery by inducing general anesthesia,establishing cardiopulmonary bypass, and inducing arrest of cardiacfunction. Devices and techniques for inducing arrest if cardiac functionand establishing cardiopulmonary bypass are described in co-pendingapplication Ser. Nos. 08/282,192, filed Jul. 28, 1994, 08/159,815, filedNov. 30, 1993, and 08/173,899, filed Dec. 27, 1993, which areincorporated herein by reference. After general anesthesia is induced,cardiopulmonary bypass is initiated by placing a venous cannula in amajor peripheral vein, such as a femoral vein, and placing an arterialcannula in a major peripheral artery, such a femoral artery. The venousand arterial cannulae are connected to a cardiopulmonary bypass systemwhich includes an oxygenator for oxygenating blood withdrawn from thepatient through the venous cannula, a filter for removing emboli fromthe blood, and a pump for returning the blood to the patient's arterialsystem through the arterial cannula.

With cardiopulmonary bypass established, cardiac function is arrested.Although conventional, open-chest, external aortic cross clamping andaortic cannulation through the aortic wall may be utilized, closed-chestclamping and cardioplegia delivery techniques are preferred. Asdescribed in the aforementioned copending applications, arrest ofcardiac function may be induced on a patient by introducing an aorticcatheter into a femoral artery or other major peripheral artery,transluminally positioning the distal end of the aortic catheter in theascending aorta, and expanding the occluding member 110 (FIG. 13) toocclude the ascending aortic lumen between the coronary ostia and thebrachiocephalic artery. A cardioplegic agent, preferably a potassiumchloride solution mixed with blood, is delivered through a lumen of theaortic catheter into the ascending aorta where the cardioplegic fluidflows into the coronary arteries thereby perfusing the myocardium andarresting cardiac function. A venting catheter may be introduced intothe right side of the heart or into the pulmonary artery from aperipheral vein, as described in copending application Ser. No.08/415,238, filed Mar. 30, 1995, which is incorporated herein byreference. In addition, a retrograde cardioplegia catheter may beintroduced from another peripheral vein into the coronary sinus forretrograde delivery of cardioplegic fluid through the coronary sinus. Inorder to obtain access to the heart from the right lateral side of thechest, the right lung is collapsed by inserting an endotracheal tubeinto the right main stem bronchus and applying a vacuum to deflate thelung. When requiring access to the left lateral side of the chest, whenusing for the vent needle 34 for example, the left lung is alsocollapsed.

With cardiac function arrested and the patient's circulation supportedby extracorporeal cardiopulmonary bypass, the patient is ready for amedical procedure such as a mitral valve repair or replacement.Referring to FIG. 1, the instrument delivery members 2 and 6-10 arepositioned in the chest to provide access into the chest cavity. In mostcases, two to six instrument delivery members 2, 6-10 are required. Theinstrument delivery members 2, 6-10 are configured for placement withinan intercostal space without requiring significant retraction of theribs. To introduce the instrument delivery members 2, 6-10 a smallpuncture or incision is made in the intercostal space at the desiredlocation and, with an obturator positioned therein, the instrumentdelivery members 2, 6-10 are advanced through the puncture or incision.

With the instrument delivery members 2, 6-10 in position, surgery maybegin. Much, if not all, of the procedure may be carried out underdirect vision by illuminating the chest cavity with a light source orlight guide positioned in one of the instrument delivery members. Afiberoptic bundle may also be attached to or embedded in the wall of oneof instrument delivery members to transmit light into the chest from alight source outside the chest in the manner disclosed in copendingapplication Ser. No. 08/227,366, filed Apr. 13, 1994, which isincorporated herein by reference. In most cases, however, it will bedesirable to use the thoracoscope 14 to provide illumination andvisualization of the chest cavity, preferably by means of a video cameramounted to thoracoscope 14, which transmits a video image to the monitor16 (FIG. 1). The thoracoscope 14 may be a rigid thoracoscope with astraight end or an angled end such as those available from OlympusCorp., Medical Instruments Division, Lake Success, N.Y. Alternatively, athoracoscope with an articulated end steerable by means of an actuatorat the proximal end of the device may be used, such as the Welch AllynDistalVu™ (formerly Baxter DistalCamIυ 360), available from Welch Allyn,Inc., of Skaneateles Falls, N.Y.

Thoracoscopic surgical instruments are then introduced to form anopening in the pericardium. Thoracoscopic scissors and graspers are thenused to cut an opening in the pericardium. With an opening formed in thepericardium, the right lateral wall of the left atrium is in a directline of sight from the right lateral chest looking through inner lumenof instrument delivery member 2. At this time the heart is ready to beopened at an atriotomy incision in the left atrial wall between and justanterior to the pulmonary veins PV. Before making the atriotomyincision, the patient's thoracic cavity is preferably flooded with gasusing the instrument delivery members 2, 2A or 2B so that the likelihoodthe chest cavity is filled with the gas rather than air. The controlsystem 28 is activated and gas, such as carbon dioxide, is introducedinto the patient's thoracic cavity through the instrument deliverymembers 2, 2A or 2B and the temperature, pressure, humidity and gasconcentration are monitored by sensors 13 and fed back to the controlsystem 28. The vacuum pump 30 may be used to remove air during theinitial flooding or throughout the procedure. Alternatively, one of theinstrument delivery member plugs 19 may be removed so that air isinitially ejected through one of the instrument delivery members 6-10.If a gas shield is provided, the compressor, blower or fan is activatedso that the gas shield passes across the throughhole 4 of the instrumentdelivery members 2, 2A or 2B.

If the instrument delivery member is not being used for introduction ofinstruments, the second plug 62 is positioned in the throughhole 4 toprevent gas losses through the throughhole 4. The gas shield provided byinstrument delivery member 2B also prevent gas losses from the thoraciccavity.

The control system 28 automatically adjusts the temperature, gas flowrate, humidity, pressure and gas concentrations to maintainpredetermined levels. The operator of the gas delivery system 24monitors the display 152 and may manually control the various elementsof the gas delivery system 24 rather than permitting automaticadjustment. The operator may, of course, also change the predeterminedlevels for any of the parameters during the procedure. A gas flow rateof 6.0 l/min has been found to provide a 90% carbon dioxideconcentration in a model.

When the conditions in the patient's thoracic cavity are acceptable,such as the gas concentration, temperature, pressure, and humidity, thesurgeon cuts the heart to form the atriotomy. The endoscopic atrialretractor 12 is positioned in atriotomy AI and pulled anteriorly toretract atriotomy AI open. With atriotomy AI retracted, directvisualization of mitral valve MV is possible through the instrumentdelivery member 2, 2A, or 2B.

Under either direct visualization or video-based viewing using thethoracoscope 14 and monitor 16, the condition of mitral valve MV is thenassessed to determine whether the valve may be repaired or whetherreplacement is necessary. If the surgeon determines that repair issuitable, a number of repair procedures may be performed includingannuloplasty, in which an annuloplasty ring is attached around thenative valve to contract the annulus, quadrangular resection, in which aportion of a valve leaflet is excised and the remaining portions of theleaflet are sewn back together, commissurotomy, in which the valvecommissures are incised to separate the valve leaflets, shortening ofthe chordae tendonae, reattachment of severed chordae tendonae orpapillary muscle tissue, and decalcification of the valve leaflets orannulus. Several of these procedures may be performed on the same valve.In particular, annuloplasty rings may be used in conjunction with anyrepair procedures where contracting or stabilizing the valve annulus isdesirable.

If none of the repair procedures will adequately treat the diseasedvalve, the native valve is replaced with the replacement valve 20. Thetechniques for introducing and securing the replacement valve within theheart will be analogous to those described above for annuloplasty ring,and are further described in copending application Ser. No. 08/281,962,filed Jul. 28, 1994, which is incorporated herein by reference. Once aprosthetic valve of the appropriate size is identified, the valve isattached to the valve annulus.

When the annuloplasty ring or replacement valve has been secured withinthe heart, the atriotomy AI is ready for closure. Before, during andeven after closure of the atriotomy, the heart is preferably vented toremove gas from the heart. Before filling the heart with blood, asurfactant, such as the phospholipid pulmonary surfactant found in thelung, may be introduced into the thoracic cavity. Furthermore, theamount of retained air or gas may be observed using transesophagealechocardiography (TEE). A description of using TEE for locating retainedair in the heart is disclosed in Orihashi et al. “Retained IntracardiacAir in Open Heart Operations Examined by TransesophagealEchocardiography”, Ann Thorac Surg 55:1467-71 (1993) and Oka et al.“Detection of Air Emboli in the Left Heart by M-Mode TransesophagealEchocardiography Following Cardiopulmonary Bypass,” Anesthesiology63(1):109-3 (1985), which are incorporated herein by reference.

The needle vent 34, vent 78 and/or left ventricle vent 104 arepositioned in the left ventricle and the aortic vent 106 is positionedin the ascending aorta. The needle vent 34 preferably has a manuallymanipulatable bulb (not shown) for withdrawing gas from the leftventricle. Alternatively, the needle vent 34 may be coupled to thevacuum pump 30. Referring to FIG. 17, the vent 38 is preferablypositioned through the replacement valve, or through the native mitralvalve, when a repair is performed, so that the left ventricle can beflood with a gas, such as carbon dioxide, and vented before atriotomyclosure.

Before removing gas in the left ventricle, gas in the ascending aorta ispreferably vented using the aortic vent 106. The patient is tilted feetdownward so that gas in the left ventricle and ascending aorta migratestoward the occluding member 110. The aortic vent 106 is then used tovent gas around the ascending aorta. Referring to FIG. 13, the aorticvent 106 is preferably rotated so that the opening 114 circumscribes theoccluding member 110 between the occluding member 110 and the aorticlumen. Although it is preferred to provide both the aortic vent 106 andleft ventricle vent 104, both the aorta and left ventricle may be ventedwith the same catheter. The heart is preferably mechanically manipulatedduring venting of the various chambers in the heart in a manner similarto the open-chest procedures except that the mechanical manipulatorsextend through the instrument delivery members 2, 6-10. A discussion ofconventional de-airing procedures is described in Taber et al.“Prevention of air embolism during open-heart surgery: A study of therole of trapped air in the left ventricle” Surgery 68(4):685-691 (1970)and van der Linden and Casimir-Ahn, “When Do Cerebral Emboli AppearDuring Open Heart Operations? A Transcranial Doppler Study,” Ann ThoracSurg 51:237-41 (1991) which are incorporated herein by reference.

After removing gasses from the ascending aorta, the patient is thentilted head downward so that gas in the left ventricle rises to the apexwhere the gas can be removed using the needle vent 34, vent 78 or leftventricle vent 104. The gas at the apex of the left ventricle is thenvented. When using the needle vent 34, the needle vent 34 is preferablymoved to various other locations in the heart where pooled air may be aproblem or where ultrasound or fluoroscopy have identified pooled air orgas. Other locations where the needle vent may be used include the rightupper pulmonary vein, the right coronary sinus of Valsalva, the leftatrial appendage, which may be also be inverted or closed with sutures,and the left upper pulmonary vein.

The atriotomy is then preferably closed using thoracoscopic needledrivers and a curved needle on a suture. Alternatively, an endoscopicstapling device such as an AutoSuture™ Powered Multifire Endo TA60,available from United States Surgical Corp. of Norwalk, Conn., or anendoscopic fascia stapler, may be inserted through an anteriorinstrument port and positioned around atriotomy AI to drive a series ofstaples into the atrial wall to close the atriotomy. The opening formedin the pericardium may be closed with sutures or staples in a mannersimilar to that used for closing atriotomy AI. However, in most cases,closure of the pericardium is not necessary, and the opening may be leftwithout adverse effect.

To complete the operation, cardiac function is then restored bydiscontinuing delivery of cardioplegic fluid, terminating occlusion ofthe ascending aortic lumen, and perfusing the myocardium with warmblood. When the occluding member 110 is used, the occluding member 110is deflated and warm blood is allowed to flow into the coronaryarteries. If sinus rhythm does not return immediately, electricaldefibrillation is used to stimulate the heart and/or pacing leads may beused to pace the heart for a period of time. Once the heart is beatingnormally, the aortic catheter is removed from the patient along with anyventing catheters or retrograde cardioplegia delivery catheter which mayhave been used. Chest tubes may be inserted into the chest to providedrainage. The patient is then weaned from cardiopulmonary bypass, andthe arterial and venous cannulae are removed from the patient.

Another preferred method of minimizing the risk of air embolism is nowdescribed. The method described above generally provides a gas, such ascarbon dioxide, when the heart is initially opened so that air cannotenter the heart during the procedure. As an alternative, the gas may beinjected into the patient when the first instrument delivery member 2,6-10 is inserted into the patient. In this manner, air is prevented fromentering the thoracic cavity throughout the procedure.

In yet another preferred method, the gas may be used to displace air inthe thoracic cavity and the heart just before the atriotomy is closed.The gas may be introduced through the instrument delivery member 2, 2Aor 2B, vent 78, or needle vent 34. When using the vent 78, the vacuumpump 30 may be used to withdraw air which is displaced by the gas. Thegas concentration is monitored so that the gas concentration is at anacceptable level before closing the atriotomy. In this manner, theamount of time the thoracic cavity is exposed to the gas is minimized.

Referring to FIG. 18, another embodiment of an apparatus for preventingair embolism when performing a procedure in a patient's thoracic cavityis shown. An enclosure 158 extends around the patient and is supportedby an operating table 160. A drape 162 extends around the patient'schest and provides a substantially air-tight seal. The drape 162 mayinclude an adhesive strip (not shown) for forming the substantiallyair-tight seal. The enclosure 158 includes a number of arm pass-throughs164 on both sides of the enclosure 158. The arm pass-throughs 164 aresubstantially air tight and permit the surgeon to perform procedures inthe enclosure. A tool box 166 is slidably coupled to the exterior of theenclosure 158 for passing tools into the enclosure 158. An advantage ofthe enclosure 158 is that a retractor 118 may be mounted to theenclosure 158. The enclosure 158 is preferably coupled to the gasdelivery system 24 and control system 26 described above in connectionwith the previously disclosed embodiments via a line 168. The enclosure158 is particularly useful when providing a pressure in the enclosure158 which is higher than the pressure outside the enclosure 158 so thatair does not enter the enclosure 158. The enclosure 158 also minimizesthe amount of gas which is released into the operating room so thatsurgeon exposure to the gas is minimized.

It is understood that while the invention has been describedspecifically in the context of mitral valve repair and replacement, thedevices and methods disclosed herein will have equal application to anumber of other procedures on a patient's cardiovascular system.Furthermore, the preferred embodiments are developed as merely preferredembodiments of the invention and modifications may be made which fallwithin the scope of the invention as defined by the claims. For example,the gas outlets may be angled toward the proximal end with baffles toredirect the gas toward the distal end, the gas outlets which passacross the throughhole may contact a baffle which directs the gas towardthe distal end, the gas outlet may simply be a hose which is clipped tothe sidewall or any other part of the instrument delivery member so longas the gas outlet is coupled to the remainder of the instrument deliverymember, and the left ventricular vent may include only one lumen ratherthan two. In addition, although it is preferred to place the patient oncardiopulmonary bypass when performing procedures the present inventionis equally applicable to procedures in which the patient's heart is notstopped. Therefore, the above description should not be taken aslimiting the scope of the invention which is defined by the claims.

What is claimed is:
 1. A method of minimizing the risk of air emboliwhen performing a procedure in a patient's thoracic cavity, comprisingthe steps of: injecting a gas into a patient's thoracic cavity;measuring a pressure in the patient's thoracic cavity; maintaining thepressure in the patient's thoracic cavity at a pressure above thepressure outside the patient's thoracic cavity; and repairing orreplacing a valve in the patient's heart during the maintaining step. 2.The method of claim 1, wherein the valve is one of the mitral valve, theaortic valve, the tricuspid valve and the pulmonic valve.
 3. A method ofminimizing the risk of air emboli when performing a procedure in apatient's thoracic cavity, comprising the steps of: injecting a gas intoa patient's thoracic cavity; measuring a pressure in the patient'sthoracic cavity; maintaining the pressure in the patient's thoraciccavity at a pressure above the pressure outside the patient's thoraciccavity; and repairing a septal defect in the patient's heart during themaintaining step.
 4. A method of minimizing the risk of air emboli whenperforming a procedure in a patient's thoracic cavity, comprising thesteps of: injecting a gas into a patient's thoracic cavity; measuring apressure in the patient's thoracic cavity; maintaining the pressure inthe patient's thoracic cavity at a pressure above the pressure outsidethe patient's thoracic cavity; and performing a pulmonary thrombectomyon the patient during the maintaining step.
 5. A method of minimizingthe risk of air emboli when performing a procedure in a patient'sthoracic cavity, comprising the steps of: injecting a gas into apatient's thoracic cavity; measuring a pressure in the patient'sthoracic cavity; maintaining the pressure in the patient's thoraciccavity at a pressure above the pressure outside the patient's thoraciccavity; and performing electrophysiological mapping of the patient'stissue during the maintaining step.
 6. A method of minimizing the riskof air emboli when performing a procedure in a patient's thoraciccavity, comprising the steps of: injecting a gas into a patient'sthoracic cavity; measuring a pressure in the patient's thoracic cavity;maintaining the pressure in the patient's thoracic cavity at a pressureabove the pressure outside the patient's thoracic cavity; and performingcoronary artery bypass grafting on the patient during the maintainingstep.
 7. A method of minimizing the risk of air emboli when performing aprocedure in a patient's thoracic cavity, comprising the steps of:injecting a gas into a patient's thoracic cavity; measuring a pressurein the patient's thoracic cavity; maintaining the pressure in thepatient's thoracic cavity at a pressure above the pressure outside thepatient's thoracic cavity; and performing angioplasty on the bloodvessel of the patient during the maintaining step.